Understanding the structure and properties of geological formations may reduce the cost of drilling wells for oil and gas exploration. Measurements are typically performed in a borehole (i.e., downhole measurements) in order to attain this understanding. For example, such measurements may identify the composition and distribution of material that surrounds the measurement device downhole. To obtain such measurements, a variety of sensors and mounting configurations may be used.
For example, some downhole tools use electromagnetic receivers as sensors to measure formation resistivity. These include multi-component array induction tools, which use a transmitter to excite orthogonal magnetic dipoles, and electromagnetic receivers to measure the resulting field at various distances from the transmitter. This tool, which can be used to measure anisotropric resistivity (Rh, Rv) to identify formation types, and features within these formations, has been fairly successful in oil-based mud (OBM) applications. In water-based mud (WBM) applications however, success has been limited due to borehole effects that render less than reliable results whenever the borehole mud is highly conductive.